Compared with conventional light sources such as incandescent lamp, fluorescent lamp, etc., light emitting diode (LED) light sources and organic light emitting diode (OLED) light sources have the characteristics of being thin and light, mercury-free, and ultraviolet light-free, and may serve as planar light sources. Thus, LED and OLED light sources are considered as light sources that are emerging and full of potential.
FIG. 1 is a view illustrating a conventional light emitting device adopting a plurality of organic electroluminescent elements. Referring to FIG. 1, a light emitting device 100 includes a plurality of organic electroluminescent elements 110A to 110C (FIG. 1 only illustrates three of the elements), a plurality of connection circuit boards 120 (FIG. 1 only illustrates three of the boards), a power circuit 130, and a ground circuit 140.
Referring to FIG. 1, the organic electroluminescent elements 110A to 110 C are connected to one another in series through the connection circuit boards 120. In addition, the power circuit 130 provides a constant current to the organic electroluminescent elements 110A to 110C to make the organic electroluminescent elements 110A to 110C emit light.
In the light emitting device 100, since the organic electroluminescent elements 110A to 110C are connected to one another in series, when one (e.g., the organic electroluminescent element 110A) of the organic electroluminescent elements 110A to 110C malfunctions and becomes an open circuit (e.g., always-OFF state), the rest organic electroluminescent elements 110B and 110C may not emit light.
Detailed descriptions with reference to FIG. 1 are provided as follows. When the organic electroluminescent element 110A malfunctions and becomes the open circuit, the organic electroluminescent elements 110B and 110C do not emit light. When the organic electroluminescent element 110B malfunctions and becomes the open circuit, the organic electroluminescent element 110A still emits light, but the organic electroluminescent element 110C does not emit light.
In addition, when one of the organic electroluminescent elements 110A to 110C (e.g., the organic electroluminescent element 110B) malfunctions and becomes a short circuit (e.g., always-ON state), the organic electroluminescent element 110B, which is the short circuit, may become a resistor that does not emit light but consumes power. For example, when the organic electroluminescent element 110A malfunctions and becomes the short circuit, even though the organic electroluminescent elements 110B and 110C still emit light, the organic electroluminescent element 110A may still consume power.
Thus, the light emitting efficiency of the light emitting device 100 may become worse if one of the organic electroluminescent elements 110A to 110C malfunctions.
In addition, in the conventional light emitting device 100, since the organic electroluminescent elements 110A to 110C are connected in series, the light emitting device 100 needs a high driving voltage, which increases the risk of electric shock.
Besides, the light emitting device 100 of FIG. 1 does not permit cutting. Cutting in any form may lead to damages to the electrical connection of the organic electroluminescent elements 110A to 110C and thus makes the light emitting efficiency of the light emitting device 100 worse. Moreover, when the light emitting device 100 with a predetermined area is required, such device must be ordered in advance from the manufacturer. Thus, the cost of the light emitting device 100 is higher, and the time required for manufacturing the light emitting device 100 is also longer.